1. Field
The present invention is related to illumination intensity uniformity compensators.
2. Related Art
Uniformity compensators (also known as UniComs, by those skilled in the relevant art) are used in many systems, including lithography systems, for example, to provide an illumination intensity distribution that is as close as possible to a desired illumination intensity distribution. In lithography, for example, a uniform illumination intensity is desired at the substrate level. A uniformity compensator can be located in a lithography system (at an illuminator or slit, for example) to compensate for effects introduced by the projection optics. In one example, an optimal uniformity distribution provided by a uniformity compensator can be a certain non-uniform distribution.
Some previous uniformity compensators used in lithography systems compensate via gray filters, for example, for low frequency uniformity variations over the slit. This can result in non-uniformity with an undesirable high frequency variation component. In addition, some currently known uniformity compensators and compensation methods have a negative impact on dose quantization due to changing of the effective slit width and/or the number of pulses in the slit. For example, some lithography systems can compensate for higher frequencies using a finger array moving from the side into the slit. However, these systems alter the slit width and number of laser pulses in the slit locally, depending on the position of each finger. Furthermore, the illumination intensity distribution requirement for modern lithography systems is tightening. Modern lithography systems currently require illumination intensity distribution variation of less than about 0.1%.
Therefore, what is needed is an illumination intensity uniformity compensator that can compensate for high frequencies and does not substantially affect the dose quantization. What is also needed is an illumination intensity uniformity compensator that does not affect the effective slit width and allows the number of pulses in the slit to remain unchanged.